The invention relates to a drilling apparatus having spun-up outer pipes and spun-up inner pipes, which can be driven by a rotary drive and a rotary impact drive, the outer pipe being adapted for coupling at one of shank ends projecting on both sides of the rotary drive and being engageable with a striker that is mounted on the inner pipe for axial movement therewith.
Drilling apparatuses of this type are used in special underground construction, in mining and earth-moving operations and in the construction industry. They are used to form holes in rocks for insertion and fastening of anchors when various rocks are used as a foundation for construction. Such drilling apparatuses have an outer pipe string and an inner pipe string, each of the outer pipes and inner pipes having threads for making up the pipe strings. When flushing fluid is caused to pass through the interior of the inner pipes from the flushing head to the core drill bit, the flushing fluid filled with cuttings is removed to the ground surface through the space defined between the outer pipes and the inner pipes. Normally, the inner pipe is driven by a rotary impact drive, and the outer pipe is driven by a rotary drive only. This can be a problem, especially in dealing with hard rock. Accordingly, as described in DE-PS 35 03 893, the rotary impact drive for the inner string is also used to act upon the rear end of the outer string. For that purpose, the inner string has an annular shoulder for the impact engagement with the outer string. The impact mechanism can be pulled back axially with the ring shoulder, whereby the drilling apparatus can work with the outer pipes being driven for rotation only. To resolve this problem, the design according to DE-PS 35 03 893 involves gear teeth provided at the end face of the annular shoulder and at the end of the outer pipe to form a rotary coupling between the outer pipes and the inner pipes. This gearing causes another problem relating to strong wear of the annular shoulder and also of the end portions of the outer pipe, so such drilling apparatuses cannot be used for a long time. It should be also borne in mind that the annular shoulder that comes to engage the end portion of the outer pipe is also rotated together with the inner pipes. The two rotary systems are positively interconnected through the gearing.
The invention is based on the problem of providing a drilling apparatus having a design in which an outer pipe can have a rotary or a rotary percussion connected to, and driven by, the drilling apparatus.